疲劳裂纹扩展的非比例过载效应SCIEI

本工作研究了比例(Ⅰ型)过载及非比例(复合型)过载对常幅Ⅰ型疲劳裂纹扩展的影响。结果表明:Ⅰ型过载所引起的裂纹滞后扩展效应远较复合型为强。因此,在估算疲劳寿命时将零、构件实际承受的过载(大都为非比例过载)简单地当作比例过载处理,可能会过高地估计寿命,带来不安全因素。文章从Ⅰ型及复合型过载所引起的裂纹钝化、裂端塑性区的形状、尺寸及裂纹闭合等方面讨论了它们对裂纹扩展滞后效应的影响。     

应用Ritz向量方法计算非比例阻尼问题

非比例阻尼问题，在结构动力分析中普遍存在。本文应用子空间Ｒｉｕｚ向量叠加方法，有效地降低了计算工作量并提高了精度     

基于临界面理论的多轴等效应变疲劳寿命预估模型

针对等效应变模型未考虑非比例附加强化影响这一不足,将最大剪切应变幅所在平面定义为临界面,引入剪切平面上的最大正应力、正应变变程以及相位差作为损伤参量来反映非比例加载条件下的附加强化效应,该损伤参量还考虑了临界面上的最大正应力和正应变变程对材料裂纹萌生和扩展的影响。采用16MnR、GH4169、S460N、45钢和Pure Ti五种薄壁圆管试件来验证模型的正确性和有效性,并与三种经典模型进行对比分析,结果表明,新模型的预估能力要优于其他三种模型,且寿命预测结果较为精确。     

计及阻尼影响的悬置系统响应解耦优化

为实现计及阻尼影响的动力总成悬置系统的解耦,建立了包含阻尼系统的动力总成悬置系统模型,计算了比例和非比例阻尼影响下的系统响应,根据悬置系统的响应特性和解耦优化原理,提出了响应解耦法。以怠速频率下100％扭矩轴响应解耦和固有频率的合理配置为优化目标,利用mode FRONTIER软件对悬置系统进行解耦优化,并在MATLAB中对优化后的解耦效果进行仿真验证,结果表明,在考虑非比例阻尼的情况下,所提出的解耦方法比能量解耦法的解耦效果更好。     

Non-proportional loading in sequentially linear analysis for 3D stress states

Sequentially linear analysis (SLA), a non-incremental-iterative approach towards finite element simulation of quasi-brittle materials, is based on sequentially identifying a critical integration point in the model, to reduce its strength and stiffness, and the associated critical load multiplier (λ_crit), to scale the linear analysis results. In this article, two novel methods are presented to enable SLA simulations for non-proportional loading situations in a three-dimensional fixed smeared crack framework. In the first approach, the cubic function in the load multiplier is analytically solved for real roots using trigonometric solutions or the Cardano method. In the second approach, the load multiplier is expressed as a function of the inclination of a potential damage plane and is deduced using a constrained optimization approach. The first method is preferred over the second for the validation studies due to computational efficiency and accuracy reasons. A three-point bending beam test, with and without prestress, and an RC slab tested in shear, with and without axial loads, are used as benchmarks. The proposed solution method shows good agreement with the experiments in terms of force-displacement curves and damage evolution.     

Visco-plastic constitutive model considering non-proportional hardening at elevated temperature under multiaxial loading

Based on the Chaboche unified visco-plastic constitutive model, a visco-plastic constitutive model which can take into account non-proportional hardening was proposed for nickel-base alloy at elevated temperature under multiaxial loading. In the proposed multiaxial visco-plastic constitutive model, the non-proportional hardening is considered as a change of kinematic hardening property. The kinematic hardening parameters which can evolve exponentially with the cumulative plastic strain and rotation factor resulted from loading path were proposed to take into account the non-proportional hardening at high temperature under non-proportional loading. Experimental verification showed that the proposed model can accurately predict the peak stresses and the hysteresis loop compared with the original model during the tension-torsion loading process for nickel-base alloy at elevated temperature under non-proportional loading.     

Multiaxial low cycle fatigue behavior and life prediction of CP-Ti under non-proportional stress-controlled mode

Multiaxial low cycle fatigue tests under non-proportional stress (NPSS) controlled mode were performed on commercial pure titanium (CP-Ti). Strain responses of axial and torsional channels under highly applied stress amplitudes show an initial hardening phenomenon. Non-proportional hardening coefficient of CP-Ti is independent of the controlled mode. The critical plane of CP-Ti under NPSS controlled mode is aligned with the maximum principal stress plane proved by optical microscopy observation. Optimized FSM model and KBM-PM model with mean axial and torsional strain are established. These models are further integrated into equations related to multiaxial stress ratio with high accuracy of life prediction for CP-Ti under NPSS controlled mode.     

双轴加载下冷变形Zr-4合金的循环变形行为及其微观机理

研究了冷变形Zr-4合金在双轴比例和非比例加载下的循环变形行为,结果表明:当循环应变幅较低时,Zr-4合金表现为循环初始硬化随后饱和的特征;随着应变幅提高,初期硬化后,表现为连续循环软化特征;高应变幅下,初期硬化消失,表现为急剧的循环软化.相同等效应变幅下,非比例加载下的Mises循环等效应力明显高于比例加载,表现为非比例附加硬化现象; 相位角30°时,非比例附加硬化程度最高.非比例加载下疲劳寿命低于比例加载.双轴疲劳变形亚结构TEM观察表明:当加载方式由比例加载转化为非比例加载时,疲劳位错结构由拉长的位错条带向位错缠结和位错胞转化,材料内部各向同性强化机理加强是Zr-4合金非比例潜在硬化的原因.     

Review: Energy Methods for Multiaxial Fatigue Life Prediction

综述:多轴疲劳寿命预测中的能量法

仲政¹，芦迎亚²

（1.哈尔滨工业大学(深圳) 理学院，广东 深圳518055；2.联合汽车电子有限公司，上海201206）

摘要：材料和结构的疲劳断裂是工程应用中最常见的失效模式之一。多轴非比例加载下，大量材料表现出非比例强化效应，疲劳寿命大大减少。本文综述了多轴疲劳寿命预测中的能量方法，能量方法被分为三类：不考虑路径效应的能量方法、与临界面法相结合的能量方法、考虑路径效应的能量方法。在三类方法中，本文着重介绍了考虑路径效应的能量方法，因为该方法能够反映多轴疲劳问题中的非比例强化效应。

关键词：多轴疲劳，寿命预测，塑性功，非比例因子

     

求解弱非比例阻尼系统实模态解的阻尼矩阵摄动法

提出了一种求解弱非比例阻尼振动系统实模态解的摄动方法和将非比拟阻尼矩阵分解为比例阻尼矩阵和余项阻尼矩阵的方法.对于弱非比例阻尼振动系统,通过同时对阻尼矩阵和响应矢量进行小参数摄动,将原非比例阻尼系统分解为一系列的比例阻尼振动系统,在此基础上用正则模态变换将各阶比例阻尼的摄动方程解耦,从而求得原非比例阻尼振动系统的近似解析解.计算实例表明,此方法的结果与数值计算结果十分吻合.